Tufting machine stop motion embodying light beam and sensor with triggering circuit responding to yarn breaks

ABSTRACT

A multi-needle carpet tufting machine receives yarn ends through a guide and feed roll system from a supply beam or an overhead creel. One or more light beam or ray energy sources and coacting photoconductive detector units are so positioned with relation to the machine that a broken yarn end at substantially any point in the system will cause interruption of a light beam and instant activation of an electronic triggering circuit which may be wired directly into the motor control switch of the machine to stop the machine. Many common difficulties with tufting machines are thus overcome.

Unite States Patent Jackson 1 51 3,687,095 Aug. 29,1972

[72] Inventor: Wilbur Jackson, PO. Box 239,

Chatsworth, Ga. 30705 [22] Filed: July 1, 1970 [21] App1.No.: 51,591

521 US. c1. ..112/79 R, 112/219 A, ZOO/61.18, 28/51, 250/219 s 51 rm. c1 ..D05c 11/14, D05c 15/00 [58] Field ofSearch....l12/79 R, 79 A, 80, 266, 410, 112/218, 219; 250/216, 219 S; ZOO/61.13, 61.18; 19/25; 28/51; 57/81; 66/161, 163',

3,094,855 6 1963 Vossen ..200/61.18 x 2,457,362 12/1948 Giglio ..112/218 R 2,438,365 3/1948 Hepp et a1. ..66/163 2,711,093 6/1955 Edelman et a1. ..139/353 x 2,967,947 1/1961 Flook, Jr ..28/51 x 3,401,267 9/1968 Engle et al ..139/353 3,530,690 9/1970 Nickell er al. ..66/163 Primary Examiner-James R. Boler' Attorney-B. P. Fishbume, Jr.

57 1 ABSTRACT A multi-needle carpet tufting machine receives yarn ends through a guide and feed roll system from a supply beam or an overhead creel. One or more light beam or ray energy sources and coacting photoconductive detector units are so positioned with relation to the machine that a broken yarn end at substantially any point in the system will cause interruption of a light beam and instant activation of an electronic triggering circuit which may be wired directly into the motor control switch of the machine to stop the machine. Many common difficulties with tufting machines are thus overcome.

8 Claims, 6 Drawing Figures PATENTEDMIBZB I912 3.687.095

SHEEI 1 UF 2 floooonnu INVENTOR WILBUR JACKSON ATTORNEYS PATENTED M1929 I972 SHEET 2 [1F 2 TUFTING MACHINE STOP MOTION EMBODYING LIGIITBEAM AND SENSOR WITH TRIGGERING CIRCUIT RESPONDING TO YARN BREAKS The main objective of the invention is to provide a more reliable, more simplified and economical stop motion for carpet tufting machines and the like. When a yarn end breaks adjacent to one needle of the machine and hangs loose, it is vital that the machine be stopped immediately as there is a tendency for the loose yarn end to enter the eye of the nearest needle, and continuing operation of the machine will sew two ends of yarn into the fabric base by means of one needle. This is an old annoying fault of tufting machines.

In the prior art, stop motions for various textile, sewing and tufting machines are known and most of these are electro-mechanical devices involving a relatively large number of moving parts and sometimes requiring quite delicate adjustment. Such prior art stop motions are expensive to build and maintain and they frequently lack delicate sensitivity particularly as needed on' a large tufting machine which may be tufting yarn loops into a fabric base up to 16 feet in width with many hundreds of needles operating simultaneously. In such a machine, a break in a single yarn or a cone or creel runout must be detected instantly and the machine must be stopped almost instantly to avoid serious mends in the product, time consuming rethreading and other difficulties well known to the art.

By means of the present invention, a greatly simplified, highly reliable and economical stop motion for industrial tufting machines is provided which will respond unfailingly to a broken yarn end anywhere between the supply beam or creel and the needles to stop the machine quickly before serious and costly damage occurs. The present stop motion embodies a light beam and detector system operating in conjunction with a solid state electronics triggering circuit which is wired directly to the motor control switch for the machine. If desired, the triggering circuit can be wired into a more sophisticated stop mechanism of the type disclosed in my prior copending application Ser. No. 790,017, filed Jan. 9, 1969, now U.S. Pat. No. 3,529,560. In either case, beams of light or ray energy are positioned strategically with relation to the yarn ends and the guide and feed roll means therefor. When a break occurs at almost any point in the system, either a broken end will fall into a light beam or a loop of yarn will be quickly formed and will enter a light beam to break the same. In either case, the light sensitive detector will activate the triggering circuit and through this circuit the stop motion mechanism in whatever form employed on the machine and the machine will stop. To render the light beam stop motion even more effective, a means is provided to direct a continuousstream of air in one direction toward the needles to'assure that broken ends at this region will not have an opportunity to become threaded into adjacent needles. Additionally, a static eliminator unit is positioned on the machine in close proximity to a straight run section of Other detailed features of the invention will be discussed during the course of the following description.

The term light as used herein encompasses white light and laser light, and the terms light detector" or sensor" cover various forms of photoconductive elements or cells.

BRIEF DESCRIPTION OF DRAWING FIGURES FIG. 1 is a fragmentary vertical section through a tufting machine having the light operated stop motion embodying the invention thereon.

FIG. 2 is a fragmentary vertical section similar to FIG. 1 illustrating the action of a broken yarn end near DETAILED DESCRIPTION Referring to the drawings in detail wherein like numerals designate like parts, a generally conventional carpet tufting machine is illustrated having a main head 10 disposed above the machine bed 11 over which a suitable fabric base 12 is conveyed by conventional feed rolls 13. Varying numbers of feed rolls for the fabric base or backing may be utilized and the arrangement in the drawings is illustrative only. As is well known, the purpose of the tufting machine is to affix a multitude of loops or tufts 14 in the fabric base 12 to produce a carpet or the like. The multitude of yarn ends 15 are carried by a corresponding number of needles 16 into and through the fabric base 12 and a conventional oscillating looper means 17 beneath the machine bed 11 and mounted on a rocker shaft 18 coacts with the machine needles in a well known manner to produce the loops or tufts 14. A hook or looper 19 is provided on the means 17 for each invarious elements of the system coact in a unique manner toward the end of providing a completely practical and satisfactory stop motion for a carpet tufting machine.

dividual' needle and there also may be provided adjacent each looper a cutter to sever the loops 14 when a severed carpet pile is desired instead of a loop pile. All of this is conventional and need not be described further.

The several needles 16 are all carried by a vertically reciprocating needle bar 20 shown in the full down position in FIG. 3 and full up in FIG. 1. The needle bar and needles are caused to reciprocate vertically by the operation of a main rotary shaft 21 extending through the head 10 having eccentric means 22' thereon to operate connecting rod means 23 and vertical reciprocating rods 24 to which the needle bar 20 is attached, the rods 24 operating within guide bearings 25 on the machine head. All of this structure is conventional in tufting machines.

In'the embodiment shown, the multitude of yarn ends 15 are drawn from a yarn beam or spool, not

shown, spacedbeyond one side of the machine at a relatively low elevation. In response to the demand of the needles 16, the yarn ends are drawn upwardly from the beam and pass through openings in a pair of spaced horizontal yarn guides 26 and 27 which are suitably supported in fixed relation to the machine above and beyond the forward side of the head 10. The yarn ends travel in horizontal sections 28 between these two guides and then engage a system of yarn feed rolls 29 near the top of the head and near the forward side thereof. The feed rolls 29 are conventional and may vary in number, four such rolls being quite common, as illustrated. After leaving the feed rolls 29, the yarn ends pass downwardly substantially vertically at 30 close to the forward side of the head 10 and pass through guide openings in another fixed yarn guide 31 attached to the machine head.

Somewhat below the guide 31, the yarn ends are engaged by adjustable power driven yarn pulling rolls 32 which constitute an important feature of the invention believed to be essential for efficient operation of the stop motion. These yarn pull rolls are not conventional in tufting machines and have special application in the invention. Their surfaces are toothed or fluted as indicated at 33 for positive engagement with the yarn ends passing therebetween. The pull rolls are suitably supported and joumaled on the head 10 by bearings 34 and one set of rolls is laterally adjustable relative to the opposing roll, as shown by the horizontal arrow in FIG. 5. The adjusting means may be conventional, such as a slot and set screw. By this means, the degree of interrneshing of the flutes 33 may be varied to regulate the positive feeding or pulling of the yarn. As will be pointed out further, the yarn pull rolls 32 are required toassure the formation of a loop which will interrupta light beam when a yarn end breaks at a needle. Referring to FIG. 3, the pull rolls 32 are driven by gearing 35 having a connection with the drive gearing 36 of yarn feed rolls 29,'the latter being driven in a customary manner from power take-off gearing 37 from the main drive shaft 21. The main drive shaft, in turn, is driven by gearing 38 operated by the tufting machine motor 39. Another take-off 40 from the main drive shaft 21 operates transmission means 41 to drive the lower feed rolls 13 for the fabric base or backing.

Immediately below the pull rolls 32, the yarn ends 15 assume a slanting attitude at 42 relativelyclose to the head 10 and at the lower end of the stretch 42 they engage a lower fixed yarn guide 43 on the tufting machine head which is well below the pull rolls 32 and inwardly or rearwardly thereof. After leaving the guide 43, the yarn ends engage a thread jerker 44 attached to the needle bar and may also engage a further guide 45 on the needle bar close to the needles, from whence the yarn ends enter the eyes of the needles 16.

Close to and rearwardly of the diagonal stretch 42 a conventional static eliminator unit 46 is mounted on the machine head 10 so that the yarns ends pass adjacent to this unit and are relieved of their static charge which eliminates sticking, clinging and mutual attraction. Such units are well known in the art and one in wide use is manufactured and sold by Herbert Products, Inc. Another feature that contributes to the overall effectiveness of the stop motion and the sensitivity thereof or reliability is the provision on the tufting machine of an air blower 47 having a conduit 48 leading to a horizontal tubular air nozzle 49 slightly rearwardly of the needles 16 and near and above the machine bed 11. The nozzle 49 has a discharge slot 50 one needle. This has been a troublesome problem with tufting machines whenever yarn breakage occurs.

The stop motion means further comprises a photoconductive detector or sensor 51 fixedly mounted immediately below and slightly forwardly of the lower fixed yarn guide 43 and near one end of the needle bar, FIG. 3. Beyond the other end of the needle bar at the same elevation is a 45 light reflector 52, above which and forwardly or outwardly thereof is positioned a similar reflector 53 to receive an upper horizontal light beam 54 from a light source 55, such as a laser light source. The upper beam 54 is reflected vertically and somewhat diagonally as at 56 between the two mirrors and then a lower horizontal beam 57 is reflected vertically and somewhat diagonally as at 56 between the two mirrors and then a lower horizontal beam 57 is reflected horizontally to the sensor 51. Thus, two horizontal light beams are produced, the upper one of which is located just below the horizontal stretch of yarn ends and the lower one 57 just under and outwardly of the yarn guide 43. In some cases, the elements 51 and 55 may be reversed with the same results. In still other cases, white light sources and detectors may be used to produce two light beams at the locations of the laser beams 54 and 57. In the case of white light, one well known device contains the source and detector in one unit and an opposing reflector is spaced at any desired point away from this unit. Therefore, instead of the elements 51 and 55 of the laser system, a pair of the combined white light source and detector units would be used in place of the units 51 and 55 with two opposing mirrors positioned at the location of the elements 52 and 53. This white light equipment is manufactured and sold by Appalachian Electronic Instruments, Inc., Ronceverte, W.Va. Other conventional photosensitive detector equipment with a white light or laser source may be employed as found desirable within the scope of the invention.

The stop motion means further includes a triggering circuit shown in FIG. 4 wired into the control switch of the main motor 39. Referring to FIG. 4, the photoconductive light sensor 51 is shown and this unit preferably embodies a photoconductive diode 58, a photocell or a transistor that is light sensitive. A lens 59 is also embodied in the unit 51 to properly focus the light beam 57 on the photoconductive element and this lens also helps to steady the light beam in the event of vibration of the machine. Without the lens, such vibration can affect the light beam and slightly change the resistance of the cell 58.

As long as the light beam 57 is uninterrupted and is striking the cell 58, the latter will conduct and cause a negative voltage to be applied to the base of a transistor 60 connected with the photocell 58, as shown. This causes the emitter of the transistor 60 to draw current through a resistor 61. It will be noted that the gate of a silicon controlled rectifier 62 is also connected to the emitter end of a resistor 61 through another resistor 63. As long as the emitter of transistor 60 draws current through resistor 61,there is insufficient voltage at the gate of the SCR 62 to cause it to fire. However, if they light beam 57 is interrupted as by the breaking of a yarn end at a needle 16, this will instantly cause the photocell 58 to lower the amount of negative voltage being applied to the base of transistor 60 so that the emitter of the transistor draws less current through resistor 61, which in turn causes an increase in positive voltage at the emitter end of resistor 61, causing SCR 62 to fire since this voltage is applied to the gate of the SCR through resistor 63. When the SCR fires, this pulls in a relay 64. Since the contacts 65 and 66 of relay 64 are connected in series with a holding coil 67 for motor control switch 68, and since the contacts 65 and 66 open when relay 64 is pulled in, this will cause the holding coil 67 to release the contacts of switch 68 and open the same to thereby stop the tufting machine motor 39. No motor connections are shown in FIG. 4 for the sake of simplicity.

It will be noted that the anode of SCR 62 is connected to the coil 69 of relay 64 and the other side of this coil is connected to the positive side of a 12 volt DC supply 70 through contacts 71 and 72 of a relay 73. When the broken yarn end that interrupted the light beam 57 is repaired, the motor 39 is restarted by pressing push button start switch 74, momentarily causing relay 73 to pull in, thereby opening contacts 71 and 72 of relay 73, which in turn breaks the circuit of the SCR, thus resetting relay 64 which closes contacts 65 and 66 at the same time. Also at this time, while push button 74 is depressed, the contacts 75 and 76 of relay 73 close, applying AC voltage to holding coil 67 of motor control switch 68 which pulls in and locks the motor switch contacts closed. Thus, the motor 39 is again running normally until the light beam 57 is again broken or the push button switch 77, which is a stop switch, is manually pressed by the operator. This switch is in series with the motor switch holding coil 67, as shown.

A potentiometer 78 is placed in the circuit to adjust the sensitivity of the light sensor or cell 58. A resistor 79 is also placed in the circuit to stabilize the gate action of SCR 62. i

The above operation of the stop motion triggering circuit responds in the identical manner to an interruption of either the lower light beam 57 or the upper light beam 54. If a yarn end breaks at one of the needles 16, FIG. 2, the action of the pull rolls 32 continuing to pull the yarn end downwardly will quickly cause the formation of a forwardly bulging loop 80 and this loop will sag and enter the lower light beam 57 and break the same, thus causing the photoconductive element 58 to initiate the action of the triggering circuit, as described, which results in stopping the motor 39. The relationship of the pull down rolls 32 to the lower yarn guide 43 and the axis of the light sensor 51 is quite critical as regards the proper formation of the loop 80 to interrupt the beam 57 whenever a yarn end breaks at the needle.

If a yarn end should break between the beam and the feed rolls 29 as in the stretch 28, such broken end will fall into the upper light beam 54 and in the identical manner activate the triggering circuit to stop the tufting machine motor. Should a break occur at some other point in the system as between the rolls 29 and theyarn guide 43, the loose end of yarn will fall into and break the beam 57 and stop the tufting machine.

It should be mentioned here that while FIG. 1 depicts the yarn ends being supplied from a beam source forwardly of the tufting machine, it is equally feasible to supply the yarn from an overhead creel and yarn packages above the machine. In such case, the guides 26 and 27 are usually moved somewhat to the left of and above the rolls 29 and the light source 55 and reflector 53 are correspondingly repositioned. The operation is exactly the same. If a break occurs in a yarn end coming from a cone above the upper light beam, the broken end will fall into such beam and the machine will stop. If a run-out of yarn occurs from a single package on the creel, the loose end will interrupt the upper light beam, whether laser or white light, and stop the machine.

The system is extremely simple and economical and free of substantially all mechanical moving parts requiring adjustment and maintenance. Only the auxiliary pull rolls 32 have been added to the otherwise generally conventional yarn feeding and guiding system of the tufting machine. The static eliminator 46 and the air nozzle 50 do not involve moving parts and these, items are simply refinements which increase the reliability of the system but are not absolutely essential. The arrangement is such that a breakage of a single yarn substantially anywhere in the system will cause triggering of the stop motion circuit in FIG. 4 to interrupt the running of the motor 39. While FIG. 4 shows the motor control switch 68 wired directly into the control circuit, it is equally feasible to wire in the connections of various machine stopping systems including those that cause the needle 16 to always stop in an up position clear of the backing 12.

Another feature of the invention which should be emphasized is that the very nature and simplicity of the light beam system, triggering circuit and associated elements renders the stop motion ideal to install on a tufting machine as an attachment kit without necessitating any significant mechanical design changes. This is very important in the interest of economy. Also the coaction of the pull rolls 32 with relation to the lower yarn guide 43 and the lower light beam 57, as depicted in FIG. 2, is vital to the stop motion.

FIG. 6 shows a relatively minor modification wherein either white, light or laser light elements 81 and 82, such as detector and source, are arranged within the tufting machine end frame portions 83 and 84 at substantially the same elevation as the unit 51 in FIG. 3. However, the elements 81 and 82 are not placed for wardly of the machine head, as in FIG. 1, but are inside of the front edge 85 of frame portions 83 and 84, as shown in FIG. 1. The light beam passing between the elements 81 and 82 is for the same purpose as the light beam 57 and functions in the same manner with respect to the triggering circuit of FIG. 4. As previously stated, where white light is employed, a separate 'means may be used to establish an upper white light beam in the same location as the upper laser beam 54.

It should be mentioned in connection with the disclosure of the positive feed rolls 29 that on some close ized at the front and rear of the machine. In such'cases,

duplicate stop motion systems embodying the invention are employed on the front and rear of the machines.

It is to be understood that the forms of the invention herewith shown and described are to be taken as preferred examples of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of the invention or scope of the subjoined claims;

What is claimed is:

1. In a tufting machine automatic stop motion, a main machine motor having a control switch, relay means coupled with the motor control switch to maintain it closed when the machine is in normal operation and causing opening of said switch to stop the machine in response to a broken yarn, a yarn break sensing element having an electrical output of a first level when tufting yarns are unbroken, a source of DC potential electrically connected with said sensing element and said relay means, a first semiconductor switch comprising a pair of current conducting electrodes and a control electrode, said sensing element coupled across one conducting electrode and the control electrode of said first switch and maintaining said first switch conductive while the sensing element remains energized to provide an output of said first level, a second semiconductor switch having a control electrode and a pair of conducting electrodes coupled with the relay means across said source of DC potential and being 'operatively nonconducting while said first semiconductor switch is conductive, and additionally including circuit means interconnecting the other current conductingelectrode of the first switch to the control electrode of said second switch, said first switch being operable to cause the second switch to become conductive when the first switch becomes non-conductive due to a broken yarn de-energizing the sensing element, said second switch then activating the relay means when conductive and opening the motor control switch to thereby stop the machine.

2. The structure of claim 1, and said sensing element comprising a photoconductive sensor intercepting a light energy beam from a source as the beam passes near tufting yarns in the machine.

3. The structure of claim 2, and said circuit means including a resistance element coupled between said other conducting electrode of said first switch and said source of DC potential, and another resistance element interconnecting the last-named conducting electrode of the first switch with said control electrode of the second switch.

- 4. The structure of claim 3, and said first switch comprising a transistor wherein said control electrode is the base and said conducting electrodes are the collector and emitter, said second switch comprising a controlled rectifier in which said control electrode is the gate and said conducting electrodes are the anode and cathode of the second switch.

5. The structure of claim 1, and said relay means further comprising a holding coil coupled with the motor control switch and maintaining the latter closed until the relay means is energized by the conductivity of the second semiconductor switch.

6. The structure of claim 5, and said relay means further comprising a machine starting relay and manual switch, and ela y con act' eans which perate i response to e anua switc to restore t e secon semiconductor switch to its non-conductive state.

7. The structure of claim 4, and said resistance element including a first resistor coupled between the emitter of the first switch and one terminal of said source of DC potential, said another resistance element including a second resistor coupled between the emitter of the first switch and the gate of the second switch, a third resistor coupled between said photoconductive sensor and second resistor, and a fourth resistor coupled between said gate of the second switch and the other terminal of said source of DC potential.

' 8. In a carpet tufting machine, a reciprocating needle bar carrying a plurality of needles having eyes adapted to receive a like number of yarns from a remote source,

guide means for the yarns between said source and needles to maintain the yarns onpredetermined definite paths to the needles, continuously positively driven interrneshing fluted feed rolls for the yarns between said source and needles and upstream from the guide means, said feed rolls continuing to positively feed all of the yarns when a break occurs in one or more of the yarns between the feed rolls and needles to cause the immediate formation of a slack yarn loop or loops in the broken yarns, said guide means and feed rolls being offset laterally relative to each other and on one side of the needle bar so that said slack yarn loop or loops will be formed outwardly and downwardly with respect to the guide means and needle bar, a light beam generator and a coacting photoelectric sensor mounted near and laterally outwardly of the guide means and slightly below the guide means and substantially directly below the feed rolls, whereby said slack loop or loops formed by the continuous operation of the feed rolls will unfailingly enter the light beam which passes between the beam generator and photoelectric sensor transversely of the yarns and near the yarns, and electrical stop motion means for the tufting machine including a tufting machine main motor control switch and an electronic triggering circuit coupled with said control switch and said photoelectric sensor, said stop motion means being activated whenever any one of said slack yarn loops falls into said light beam and interrupts the beam. 

1. In a tufting machine automatic stop motion, a main machine motor having a control switch, relay means coupled with the motor control switch to maintain it closed when the machine is in normal operation and causing opening of said switch to stop the machine in response to a broken yarn, a yarn break sensing element having an electrical output of a first level when tufting yarns are unbroken, a source of DC potential electrically connected with said sensing element and said relay means, a first semiconductor switch comprising a pair of current conducting electrodes and a control electrode, said sensing element coupled across one conducting electrode and the control electrode of said first switch and maintaining said first switch conductive while the sensing element remains energized to provide an output of said first level, a second semiconductor switch having a control electrode and a pair of conducting electrodes coupled with the relay means across said source of DC potential and being operatively non-conducting while said first semiconductor switch is conductive, and additionally including circuit means interconnecting the other current conducting electrode of the first switch to the control electrode of said second switch, said first switch being operable to cause the second switch to become conductive when the first switch becomes non-conductive due to a broken yarn de-energizing the sensing element, said second switch then activating the relay means when conductive and opening the motor control switch to thereby stop the machine.
 2. The structure of claim 1, and said sensing element comprising a photoconductive sensor intercepting a light energy beam from a source as the beam passes near tufting yarns in the machine.
 3. The structure of claim 2, and said circuit means including a resistance element coupled between said other conducting electrode of said first switch and said source of DC potential, and another resistance element interconnecting the last-named conducting electrode of the first switch with said control electrode of the second switch.
 4. The structure of claim 3, and said first switch comprising a transistor wherein said control electrode is the base and said conducting electrodes are the collector and emitter, said second switch comprising a controlled rectifier in which said control electrode is the gate and said conducting electrodes are the anode and cathode of the second switch.
 5. The structure of claim 1, and said relay means further comprising a holding coil coupled with the motor control switch and maintaining the latter closed until the relay means is energized by the conductivity of the second semiconductor switch.
 6. The structure of claim 5, and said relay means further comprising a machine starting relay and manual switch, and relay contact means which operate in response to the manual switch to restore the second semiconductor switch to its non-conductive state.
 7. The structure of claim 4, and said resistance element including a first resistor coupled between the emitter of the first switch and one terminal of said source of DC potential, said another resistance element including a second resistor coupled between the emitter of the first switch and the gate of the second switch, a third resistor coupled between said photoconductive sensor and second resistor, and a fourth resistor coupled between said gate of the second switch and the other terminal of said source of DC potential.
 8. In a carpet tufting machine, a reciprocating needle bar carrying a plurality of needles having eyes adapted to receive a like number of yarns from a remote source, guide means for the yarns between said source and needles to maintain the yarns on predetermined definite paths to the needles, continuously positively driven intermeshing fluted feed rolls for the yarns between said source and needles and upstream from the guide means, said feed rolls continuing to positively feed all of the yarns when a break occurs in one or more of the yarns between the feed rolls and needles to cause the immediate formation of a slack yarn loop or loops in the broken yarns, said guide means and feed rolls being offset laterally relative to each other and on one side of the needle bar so that said slack yarn loop or loops will be formed outwardly and downwardly with respect to the guide means and needle bar, a light beam generator and a coacting photoelectric sensor mounted near and laterally outwardly of the guide means and slightly below the guide means and substantially directly below the feed rolls, whereby said slack loop or loops formed by the continuous operation of the feed rolls will unfailingly enter the light beam which passes between the beam generator and photoelectric sensor transversely of the yarns and near the yarns, and electrical stop motion means for the tufting machine including a tufting machine main motor control switch and an electronic triggering circuit coupled with said control switch and said photoelectric sensor, said stop motion means being activated whenever any one of said slack yarn loops falls into said light beam and interrupts the beam. 